Research objectives for the coming year are: 1. Characterization of viral genomes present in AMV preparations. 2. Purification of newly synthesized supercoiled proviral DNA isolated from recently infected chicken cells. 3. Identification and arrangement in unintegrated provirus of DNA fragments generated by restriction endonucleases. 4. Topology of endogenous proviral DNA in the genome of normal chicken cells from specified chicken strains, RAV-O-producing or nonproducing. 5. Topology of AMV provirus in the genome of leukemic myeloblasts induced by AMV and in the genome of nontransformed but virus-producing chick embryonic fibroblasts.